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105/04/10

Expeditionary Systems Evaluation DivisionNSWC Crane Division Detachment Fallbrook

Pyrotechnic Shock Loadingof the

M82 Percussion Primer in theM777 Light Weight Howitzer Magazine Assembly

Presented to theNDIA Joint Armaments Conference

May 2010

205/04/10


Co-Authors• Dr. Ryan Olsen, T&E Board Chairman, NSWC Crane, Detachment

Fallbrook, ESED• Kathryn Hunt, Chemical Engineer, USMC MARCORSYSCOM, PM

Ammo• Mr. Victor Hugo, Mechanical Engineer, NSWC Crane, Detachment

Fallbrook, ESED• Mr. Jon Conner, Senior Scientist, National Technical Systems,

Dana Point, CA• Mr. Caleb Bell, Program Manager, National Technical Systems,

Camden, AR

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Pyrotechnic Shock Loading of the M82 Percussion Primer in the M777 Light Weight Howitzer Magazine Assembly

• Background– M82 Percussion Primer Description and Design– M777 Primer Feed Mechanism– Premature Primer Functioning Observations– Test Design and Objective

• Evaluation of Operational Loading of M777 Magazine Assembly– Instrumentation Description– Field Test Firing Schedule– Data Reduction/Signals Analysis

• Simulation of Operational Loading with Laboratory Shock Tests– Baseline Sensitivity Test– Pyrotechnic Shock– Sine Burst– Drop Shock

• FEA and Test Results• Summary and Conclusions

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M82 Percussion Primer Description

– US Army and Marine Corps standard primer for the initiation of all 155mm Howitzers

– During functioning, black powder output ignites propelling charge

– On earlier Howitzers the primer was hand loaded into breach– New Howitzer designs incorporate a mechanical loading

assembly

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M82 Percussion Primer Design

PLUNGER

PRIMER

BODY

PRIMER CHARGE (BLACK POWDER)

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M777 Howitzer Primer Feed Mechanism Description

PRIMER MAGAZINE AND TRAY ASSEMBLY

PRIMER FEED ATBREACH ASSEMBLY

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Premature Primer Functioning

– During initial weapon testing, multiple primers functioned in the magazine during firing

– Field malfunctions associated with functioning of primers during chambering

– Primer is subjected to extreme forces associated to M777 firing

– Primer not designed to withstand these types of forces

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Test Design and Objective

Understand the impact of M777 firing on the M82 primer– Measure forces associated with M777 firing– Simulate these forces – Condition M82 Primers to simulated forces– Verify their functional performance and sensitivity

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Instrumentation Description

• 3 Each Endevco 2225M5A Piezoelectric Accelerometers (100,000 g’s)

• Installed on Tri-axial Mounting Block

• Mounting Block Bolted to Top of Primer Magazine Assembly

• Cables Tied Down and Routed to Side of Gun System

• Endevco 133 Charge Amplifier

• LDS Genesis Digital Data Recorder

– 125 kHz Sampling Rate

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Field Test Firing Schedule

Round Numbers

Projectile Fuze PropellingCharge

1-4 M795 HE M739A1 MACS at Increment 5

5-8 M795 HE M739A1 M203A1

9-12 M107 HE M739A1 M4A2 White Bag - Charge 7

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Data Reduction/Signals Analysis

Raw Accel Data – Z Axis

Band Pass FilterSmoothed

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Composite Acceleration Shock Response Spectra

X Axis Y Axis Z Axis

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Data Reduction/Signals Analysis Summary

• Forces compromised of 3 distinct phenomena– Shock associated with propellant combustion– Harmonics associated with projectile travelling down

barrel– Recoil force

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Data Reduction/Signals Analysis - Conclusions

• Laboratory simulation requires three techniques– Pyrotechnic Shock

– Simultaneous in all 3 axes – Based on Composite SRS

– Electro-Dynamic Shaker– 250 Hz, 200 g Sine Burst in Z axis

– Drop Test – 200 g, 10 msec Half Sine Pulse in Z axis

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Simulation of Operational Loads – Test Methodology

• Sensitivity Testing– Establish Baseline M82 Percussion Primer Lot Sensitivity– Evaluate Impact of Sequential Shock Testing on Sensitivity

• Shock Testing w/Test Fixtures to Replicate Tactical Magazine Interfaces

– 100 Primers Total– Replica Magazine Test Fixture Holds 10 Primers– 9 Shock Replications Applied to Each Group Sequentially

• Drop Shock• Pyrotechnic Shock Tests• Sine Burst Tests

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Drop Shock Testing

M82 Primers in Magazine Fixture Drop Shock Test SetupAccel Data – Z Axis

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Pyrotechnic Shock Testing

Magazine Fixture w/Accels Magazine Fixture Mounted to Resonating Plate

Det Cord Patters for Pyroshock

Example +/- SRS Response Curve

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Pyrotechnic Shock TestingPremature Function of M82 Primer

Group 5 Pre-Test Group 5 Post-Test

Group 5 SN 1 Premature Function(overstress of force)

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Sine Burst Shock Testing

Group 10 Pre-Test

Electro-Dynamic Shaker Test Setup

Example Response Accel Output

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Dynamic FEA Analysis Results

Plunger/Primer Only Model:Primer Cup Material Yield Strength Approx 17 ksi

Dynamic Shock Load Max Von Mises Stress in Primer Cup (ksi)

Z Axis Pyroshock SRS 19.8Z Axis Drop Shock 0.136Z Axis Sine Burst 0.235

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Summary and Conclusions• Operational Loading of M82 Percussion Primers During

M777 Firings Evaluated for Various Maximum Charge Configurations

– Loading consists of three aspects: pyrotechnic shock, 250 Hz harmonic burst, and recoil shock

• Pyrotechnic Shock Loading is Most Severe Aspect of Operational Loads Based on Lab Tests and Dynamic FEA Analysis

– Overstress induced premature function of primers

• Sensitivity testing of conditioned primers in progress

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